Bias-groove piston and ring therefor

ABSTRACT

A piston and compression ring therefor useful in high pressure gas compressors and expanders having self-lubricated rings. The ring is relatively narrow in its axial dimension and has an angular length from end-to-end thereof in excess of 360*, one end portion of the ring being offset axially so as to overlap the other end portion thereof and reinforce the same. The piston provides a circumferential ring groove that is enlarged axially over an angular length sufficient to seat such offset overlapping end portions of the ring therein; and the ends of the groove as defined by the axial enlargement thereof and the respectively cooperative portions of the ring are in close proximity and are all parallel so as to prevent the ring from rotating but permit it to expand as it wears without increasing the likelihood of leakage therepast. The ring and groove therefor are each biased or inclined inwardly and axially and have a somewhat frustoconical configuration.

United States Patent [1 1 Josephian 1451 *Nov. 6, 1973 1 BIAS-GROOVEPISTON AND RING THEREFOR [76] Inventor: William Josephian, 2311 MagnoliaSt., Oakland, Calif. 94607 211 Appl. No.: 183,435

Related U.S. Application Data [63] Continuation-impart of Ser. No.4,230, Jan. 20, 1970,

Pat. No. 3,656,768.

[52] U.S. Cl. 92/172, 277/167 1511 Int. Cl F16j 9/04 I58] Field ofSearch 277/167, 168, 203, 277/196, 216, 220, 236; 92/172 [56] ReferencesCited UNlTED STATES PATENTS 2,522,764 9/1950 Roberts 277/172 1,584,4705/1926 Quintenz 277/172 3,134,602 5/1964 Wilson 277/203 2,809,08010/1957 Mittell et al. 277/203 X 3,656,768 4/1919 Josephian 277/167FOREIGN PATENTS OR APPLICATIONS 474,055 10/1937 Great Britain 277/172298,259 10/1928 Great Britain ..277/172 Primary Examiner-Charles J.Myhre Assistant ExaminerR. H. Lazarus Attorney-Joseph B. Gardner [57]ABSTRACT A piston and compression ring therefor useful in high pressuregas compressors and expanders having selflubricated rings. The ring isrelatively narrow in its axial dimension and has an angular length fromend-to-end thereof in excess of 360, one end portion of the ring beingoffset axially so as to overlap the other end portion thereof andreinforce the same. The piston provides a circumferential ring groovethat is enlarged axially over an angular length sufficient to seat suchoffset overlapping end portions of the ring therein; and the ends of thegroove as defined by the axial enlargement thereof and the respectivelycooperative portions of the ring are in close proximity and are allparallel so as to prevent the ring from rotating but permit it to expandas it wears without increasing the likelihood of leakage therepast. Thering and groove therefor are each biased or inclined inwardly andaxially and have a somewhat frusto-conical configuration.

5 Claims, 4 Drawing Figures PAIENTEUnuv 6 I915 3.769.882

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F16 2 WILLIAM A TTORNEY BIAS-GROOVE PISTON AND RING THEREFOR RELATEDAPPLICATION The present application is'a continuation-in-part'of mycopending patent application Ser. No. 4,230, now U.S. Pat. No.3,656,768; filed Jan. 20, 1970.

This invention relates to a piston and ring therefor and, moreparticularly, to a piston and ring assembly for reciprocable receiptwithin a cylinder structure to slideably engage the walls thereof anddefine a pressure seal therewith. The invention is especially useful ingas compressors in which gaseous fluids are compressed to relativelyhigh pressure values and in reciprocable expanders in which highpressure gases are expanded to much lower pressure values to reduce thetemperature to cryogenic ranges.

In gas compressors and expanders of the type being considered, the ringsthereof are known as selflubricated rings and run dry so as to avoid oilcontamination, and as a consequence the pressure-seal augmentationobtained in conventionally lubricated piston-cylinder structures as aresult of the presence of a thin oil film between the piston andcircumjacent cylinder wall is lost. Also, however, the rings wear veryrapidly because of the absence of a lubricating medium, and it is notunusual for a ring to wear up to a quarter of an inch during its shortoperating life which under ideal conditions is generally restricted tofrom 1,200 to 3,000 hours. As a consequence of such wear and the highpressures to which the rings are subjected (often in the range from2,000 psi to 3,000 psi), the practice is to make the rings thick in theaxial direction (about three-eights of an inch, for example) in order toprovide sufficient strength to withstand the high gaseous pressureforces.

As explained in my aforementioned patent application, I have discoveredthatthe use of thick piston rings accelerates ring wear and theorizethat the substantial axial surface engagement of each ring with thecircumjacent cylinder wall prevents significant pressure leakage orblow-by between the contiguous surfaces of the ring and cylinder so thatthere is no active pressure force acting against the outer surface ofthe ring in opposition to the high gaseous pressure force operative withthe piston groove against the inner surface of the ring and urging itoutwardly into exceedingly tight frictional engagement with the cylinderwall, thereby increasing the rate of ring wear. In conformance with thisdiscovery, such prior application discloses an entirely differentapproach to the problem of preventing leakage past a piston ring versuslong life thereof, and generally stated, the approach taken is that ofusing a plurality of thin or narrow rings arranged so that there are nounsupported areas which would break because of ring weakness, especiallyafter substantial wear thereof.

I In structural terms, the mechanism disclosed includes a cylindricalpiston having a plurality of narrow circumferential grooves spacedaxially along the outer wall thereof, and a plurality of narrow pistonrings respectively disposed within the grooves to provide relativelygas-tight fits between the piston and circumjacent walls of the cylinderin which they operate. Each ring and the groove therefor are especiallyconfigurated to constrain the ring from angular displacements and toprovide the same with reinforcement throughout the entire lengththereof. Further, the rings fit closely to the effective ends of thegrooves so that little leakage occurs thereat. Each narrow ring permitsblow-by therepast, restricted to small quantities by the minimalpressure differential thereacross, thereby providing a pressure forceactive against the outer surface of the ring in opposition to thepressure force acting outwardly against the inner surface thereof.

The present invention is an improvement in such approach in that itfurther restricts or reduces the effectiveness of the pressure forceactive in each piston groove to force the associated ring. outwardlyinto excessively tight, wear-inducing frictional engagement with thecircumjacent cylinder wall. Structurally, the improvement includes acylindrical piston having a plurality of circumferential grooves spacedaxially along the outer wall thereof with each groove angled or biasedinwardly and axially so as to have a somewhat frusto-conicalconfiguration. Each groove is equipped with a ring having a similar orcomplementary bias so as to seat within the groove and provide arelatively gas-tight fit with the surrounding cylinder wall.

A general object of the present invention is to provide an improvedpiston and ring assembly and, in par ticular, an assembly that isespecially adapted for use without lubrication in high pressure gascompressors and expanders although in no way restricted to such use.Another object of the invention is that of providing an improved pistonand ring assembly in which each groove and the ring therefor are biasedor angled inwardly and axially to develop frictional forces operative tooppose the pressure forces active against the inner surface of the ringand tending to displace it outwardly into tight engagement with thecircumjacent cylinder wall.

Further objects, among others, of the invention are in the provision ofa ring assembly that accommodates or compensates for ring wear withsubstantially no diminution of the effectiveness of the seal definedthereby; a ring that has a long operating life without breakage; apiston and ring arrangement in which the work of establishing a pressureseal between the piston and cylinder in which it operates tends to bedistributed among a number of rings rather than concentrated in onering. as is common in conventional high pressure compressor and expanderdevices. These and other objects and advantages of the invention,especially as concerns particular features and details thereof, willbecome appar-' ent hereinafter.

An embodiment of the invention is illustrated in the accompanyingdrawing in which:

FIG. 1 is a side view in elevation of a piston and ring assembly of thepresent invention shown within'a cylinder therefor which is illustratedin section;

FIG. 2 is a broken side view in elevation of a portion of the pistonshown in FIG. 1 with the rings removed;

FIG. 3 is an enlarged, broken axial sectional view taken along the line3-3 of FIG. 2; and

FIG. 4 is an enlarged, broken axial sectional view similar to that ofFIG. 3 but witha ring positionedin the groove therefor.

The piston and ring assembly of the present invention is adapted to fitwithin a cylinder 11 of usual construction and since there is nothingspecialized inthe construction of the cylinder itself, it will not befurther described. The piston 12 of the present invention, as iscustomary, has a slightly smaller diameter than that of the cylinder 11so as to be freely reciprocable therein. The cylinder 11 is providedwith a plurality of axially spaced circumferential grooves each ofwhich, throughout most of its length, has a width suitable to receive acomplementary piston ring 13 therein with a close fit. The ring 13, asshown in FIG. 1, is somewhat longer in angular length from end-to-endthereof than the circumference of the cylinder 1 1 and piston 12, andone end portion of the ring is offset relative to the other end portionthereof, as shown at 14.

The offset end portion 14 of the ring 13 has the same circumferentialcurvature as the entire balance thereof and is offset only the thicknessof the ring. The lower side or face of the offset portion 14 liesessentially against the upper side or face of the opposite end portionof the ring. An angular neck 14a connects the offset end portion 14 ofthe ring to the balance thereof, and the location of the neck 14a mustbe so related to the adjacent end 15a of the ring that the ring can becompressed sufficiently to fit within the cylinder 11, as shown inFIG. 1. This construction provides that there is no break in thecircumference of the ring 13 abutting the cylinder wall 11, and at onelocation there are two thicknesses of ring slidably engaging the innerwall in the cylinder.

Each groove 15 in the piston 12 has a width substantially correspondingto the thickness of the ring 13 except for a section 16 of the groovewhich has an axial width sufficient to receive the two thicknesses ofthe ring throughout the angular length in which they overlap and abuteach other, as shown in the drawing. The offset, overlapping end portion14 of the ring may have a thickness that is equal to, less than, or evenmore than the thickness of the ring; and in the embodiment illustrated,the ring is of uniform axial thickness from endto-end thereof. As anexample, in a piston having an outer diameter of approximately 5.20inches, the groove 15 may have a width of five-sixteenths of an inchwhich is increased by one-eighth of an inch at the offset 16. The ringfor such groove has an axial width of nine sixty-fourths of an inch.Such offset portions 16 are angularly spaced around the piston 12 suchthat the offset portion 16 of each groove is spaced in oppositedirections at angles of 120 from the immediately adjacent grooves on itsopposite sides. Thus, the offset 16 of every third groove are in angularalignment.

The ends 16a and 16b of each groove 15 are located at the ends of theoffset 16 thereof, and they are substantially parallel to each otherinstead of being radially disposed, as explained in my aforesaidcopending patent application. The portions of each ring 13 thatrespectively cooperate with the groove ends 164 and 16b are the neck 14aand the end or terminal edge 14b, and these portions respectivelyparallel the adjacent ends 16a and 16b of associated groove 15 in closeproximity thereto a clearance of the order of 0.002 to 0.003 of an inchusually being provided. The opposite end 15a of the ring 15 underliesthe offset end portion 14 thereof adjacent the neck 14a and issubstantially parallel thereto.

The groove ends 16a and 16b may be identical or may differ one from theother as shown in the drawing. In this reference, the ends may each beformed at right angles as is the case of the end 1 6b, or they may beformed with a radius as in the case of the end 16a. Forming each of theends 16a and 16b with a slight radius (one-eighth of an inch, forexample) may be somewhat less expensive than machining them to a rightangle since the enlargement 16 can be fabricated on a milling machineusing a rotating cutter having a diameter of one-fourth of an inch. Inany case, the respectively corresponding ends 14a and 14b of the ringoffset 14 must be shaped to correspond essentially to the configurationof the adjacent groove ends 160 and 16b.

Each of the rings 13 and grooves 15 is biased or has an angularinclination in which it extends inwardly and axially relative to theaxis of reciprocation of the piston 12. Accordingly, each ring andgroove has a somewhat frustoconical configuration, as is most evident inFIG. 2. The axial inclination of the rings 13 and grooves 15 is suchthat the smaller inner end of the frustum is opposite or away from thedirection of maximum gaseous pressure exerted against the piston 12 andrings thereof, as is indicated by the directional arrows in FIGS. 1 and2. Thus, each ring tends to be urged by the gaseous pressure forcesactive within the cylinder 11 toward the left, as viewed in each of theFigures, thereby tending to press the surface 17 of each ring againstthe facing surface 18 of the associated ring 15.

As indicated hereinbefore, since the reciprocable engagement of therings 13 with the circumjacent walls of the cylinder 11 is notlubricated, the rings are conventionally formed of a material havingsome inherent lubricity, and a typical example is a material comprisingTeflon which provides the lubricity and an additive such as brass (otherexamples being carbon and glass) to provide the ring with a degree ofstrength. Such a ring is relatively soft and weak, and with the smallaxial dimensions indicated (i.e., approximately one-eighth of an inchwhich is about one-third the thickness of ordinary rings), the ringswould be subject to considerable breakage. However, in the configurationshown in the drawing, each ring 13 is supported throughout its entireangular length so that there is no unsupported area that would be highlyprone to breakage.

More particularly in this respect, the high value gaseous pressureforces act against the piston 12 from right to left as viewed in FIG. 1in the direction of the arrows associated with the legend gas pressure.In the case of a gas compressor, the piston 12 will move from left toright as viewed in FIG. 1 to compress the gaseous fluids to the highpressures desired, and in the case of an expander, the gaseous pressureforces will act against the piston 12 to displace it toward the leftwhich results in the gases doing work to reduce the pressure thereof (byway of example, a pressure reduction from about 2,300 psi down to aboutpsi). In either event, the gaseous pressure forces act against the rings13 and tend to displace the same from right to left, as seen in FIG. 1,and it will be observed that each ring 13 is reinforced or buttressedthroughout its entire length either by the underlying surface of thegroove 15 or, in the case of the free end portion of the ring, by theunderlying surface of the offset end portion 14. Accordingly, there isno unsupported ring area which could break because of the high valuepressure forces acting against the ring if such an unsupported area werepresent. Further, as the rings wear and therefore expand radiallyoutwardly to compensate therefor, the free end portion of each ringsimply moves relative to the fixed end portion 14 thereof, but suchrelative movement does not result in the development of an unsupportedring area.

Also as a result of the described construction, as a ring 13 expands totake up wear, the effective end portions 14a and 14b of the ring remainin close proximity with the groove ends 16a and 16b thereby tending toprevent leakage of fluid between the ends of the rings and grooves. Theoffset end 14 of the ring is confined within the enlarged or offsetportion 16 of the groove 15 so that the ring cannot be displacedangularly which continuously maintains the rings in their originalrelative orientations. However, the offset 14 can move ra-' diallyoutwardly (and inwardly) without changing the close fit of the ringportions 14a and 14b with the respectively adjacent ends 16a and 16b ofthe groove. Thus, as wear of a ring occurs, it expands or enlarges andthe offset portion 14 thereof moves radially outwardly in theenlargement 16 of the groove, but because of the parallel relationshipand close fit as heretofore described, no significant change in thesealing quality of the cooperative sealing relationship of the pistonandring takes place.

Considering any particular ring 13, the high value gaseous pressureforce acting thereagainst enters the groove 15 and acts radiallyoutwardly against the inner surface of the ring, thereby tending todisplace it into tight frictional engagement with the circumjacent wallof the cylinder 1 1. However, because of the angular inclination of thefacing surfaces 17 and 18 of such ring and groove, the pressure forceacting outwardly against the inner surface of the ring causes the facingsurfaces 17 and 18 to be urged into tight frictional engagement. As aconsequence, a relatively high value frictional force acts inwardlyagainst the ring with the result that it tends to resist or oppose thegaseous pressure force urging the ring outwardly.

Assuming any particular coefiicient of friction between the juxtaposedsurfaces. 17 and 18 of the respective rings and grooves, the value ofthe mechanical frictional force developed between such surfaces isdirectly related to the valueof the pressure force acting outwardlyagainst the ring. Therefore, any differences in the values of thepressure forces acting in the various grooves 15 because of the pressuregradient established over the entire length of the piston 12 areautomatically compensated by corresponding changes in the mechanicalfriction forces opposing the same so that the outward displacement ofeach ring is resisted by a frictional force developed between thecontiguous surfaces 17 and 18 having a value porportional to themagnitude of the gaseous pressure force tending to urge the ringoutwardly. As a result, excessive wear of each ring is resisted.

Reducing the thickness of the rings 13 enables a greater number of ringsto be provided along the piston 12 in the same axial length thereof. Asa typifying example, in an axial piston length of about 8 inches, thenumber of rings can be increased from about seven or eight to 12.However, since each ring is relatively narrow in axial dimension, someleakage or blow-by occurs past a substantial number of the rings but theblow-by progressively decreases in magnitude from ring to ring in adiminishing order from right to left as viewed in FIG. 1 because thepressure gradient decreases from ring to ring in that direction. Thisleakage or blow-by is desirable as heretofore explained, because itresults in a pressure force being active between the substantiallycontiguous surfaces of various of the rings and the cylinder wall, whichpressure force tends to counteract the high value pressure force presentwithin each ring groove 15 and urging the ring 13 therein outwardly intotight frictional engagement with the cylinder wall. Accordingly, suchinwardly directed,

pressure force together with the inwardly active frictional forcedeveloped between the abutting inclined surfaces 17 and 18 of any ring13 and its groove 15 effectively resist outward displacement of the ringinto excessive wear-inducing engagement with the cylinder wall.

The ring 13 at the extremity, of the right-hand end of the piston12-will have the maximum pressure force acting thereagainst and, at thesame time, the counteracting pressure force present within theassociated groove 15 will approximate such maximum pressure value. Thenext successive ring will have a somewhat lesser pressure value actingthereagainst since the maximum pressure value will be reduced by theamount of the pressure drop across the first ring 13. The pressureactive against each ring will diminish in value from ring to ring untila point is reached at which substantially no blow-by occurs, and in eachinstance the value of the pressure force operative within the groove 15of any particular ring 13 will substantially approximate the value ofthe pressure acting axially upon such ring. Accordingly, an automaticadjustment of the values of the active and counteracting pressure forcesoccurs from ring to ring. In any case, the wear experienced by each ring13 is diminished substantially over that present in conventionaldevices, and as a result, the life of such device before ringreplacement is required is significantly increased, and it is believedthat in the usual instance such increase at least doubles the usefullife of the compressor or expander device.

The construction shown. also avoids the necessity of carefully millingthe two abutting ends of the usual piston ring, of carefully millingoverlapping slots in one end of a ring to fit a tongue in the oppositemating end, or of providing othersimilar constructions found in the artwhich have been provided in an effort to avoid leakage of gas around apiston ring.

it will be understood that the drawings and the above disclosuredisclose the preferred embodiment of my invention, and that somemodifications will occur to those skilled in the art which will notdepart fromthe invention herein disclosed. Accordingly, it isintendedthat the appended claims cover such modifications as fall within thetrue spirit and concept of the invention.

What is claimed is:

l. The combination of an axially reciprocable piston and a piston ringtherefor, said ring being of substantially greater angular length fromend to end thereof than the circumference of said piston, one endportion of said ring being axially offset with respect to the other endportion thereof and disposed in overlapping adjacency therewith, saidpiston having a groove thereabout in which said ring is mounted, saidgroove having at one location therealong an axial enlargementcomplementary in axial width and angular extent to the overlapping endportions of the ring so as to accommodate the same, the terminal ends ofsaid enlargement being substantially parallel and the respectiveterminal edges of said offset end portion of said ring being in closeproximity therewith, said ring and groove having facing surfacesgenerally transverse to the axis of reciprocation of said piston andangularly disposed with respect thereto to incline inwardly and axiallytheretoward in a direction away from the direction of maximum pressuredevelopment against said piston when operative within said cylinder.

2. The combination of claim 1 in which said ring is a self-lubricatedring structurally weak and relative narrow in axial dimension, said ringbeing supported from end-to-end thereof within said groove so that nohigh value pressure forces present within a cylinder in which saidpiston and ring operate can act against an unsupported ring area tocause breakage thereat.

3. The combination of claim 1 in which the terminal edges of said offsetend portion are substantially parallel to the respectively adjacent endsof said enlargement, and in which said terminal edges and enlargementends are substantially parallel to the axis of reciprocation of saidpiston.

4. The combination of claim 3 in which the aforesaid one end portion ofsaid ring is offset bodily with respect to the entire balance thereofwhich defines a common another.

1. The combination of an axially reciprocable piston and a piston ringtherefor, said ring being of substantially greater angular length fromend to end thereof than the circumference of said piston, one endportion of said ring being axially offset with respect to the other endportion thereof and disposed in overlapping adjacency therewith, saidpiston having a groove thereabout in which said ring is mounted, saidgroove having at one location therealong an axial enlargementcomplementary in axial width and angular extent to the overlapping endportions of the ring so as to accommodate the same, the terminal ends ofsaid enlargement being substantially parallel and the respectiveterminal edges of said offset end portion of said ring being in closeproximity therewith, said ring and groove having facing surfacesgenerally transverse to the axis of reciprocation of said piston andangularly disposed with respect thereto to incline inwardly and axiallytheretoward in a direction away from the direction of maximum pressuredevelopment against said piston when operative within said cylinder. 2.The combination of claim 1 in which said ring is a self-lubricated ringstructurally weak and relative narrow in axial dimension, said ringbeing supported from end-to-end thereof within said groove so that nohigh value pressure forces present within a cylinder in which saidpiston and ring operate can act against an unsupported ring area tocause breakage thereat.
 3. The combination of claim 1 in which theterminal edges of said offset end portion are substantially parallel tothe respectively adjacent ends of said enlargement, and in which saidterminal edges and enlargement ends are substantially parallel to theaxis of reciprocation of said piston.
 4. The combination of claim 3 inwhich the aforesaid one end portion of said ring is offset bodily withrespect to the entire balance thereof which defines a common plane, theaxial enlargement of said groove being in one direction only.
 5. Thecombination of claim 1 in which said piston is provided with a pluralityof grooves each having a ring mounTed therein, the enlarged portions ofcertain of said grooves being angularly displaced with respect toanother.